Machine tool



Aug. 26, 1941.` H. F. BAKEWELL MACHINE TOOL INVENTOR, I Ecz'dUga/fewd Z1BY L) IU il 3 Sheets-Sheet 1` Filed Sept. 4, 1940 Ang. 26, 1941.

H. F. BAKEWELL.

MAGHINE mor.-

Filed sept, '4, 1940 3 Sheets-Sheet 2 INVENT OR.

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J Ill.. llll lllllul Aug 26; 1941 H. F. BAKEWELL 2,253,493

' MACHINE TOOL Filed Sept. 4, 1940 y '3 Sheets-Sheet 3 Patented Aug. 26,1941.

f UNITED STATE vsf APATif:NT oFFI-C'El- MACHINE. Toor. l neming F.Bakewell, sentiamo', cem.

I A'ppueaaen september 4, 1940, serialize. ssaz'is s claims. (ci.11i-135) This invention is a machine tool of'the type functioning byrelative rotary and axial. movement of a tool element and the work, e.g. a tapping machine; and has for an object to insure precision relativemovement of the tool ele-n ment and the work and automaticdiscontinuance of said relative movement at predetermined torquecapacity of the machine.

More particularly, it is an `object of 'the 'invention to relativelyaxially feed the tool element and the work by irrteriltting andrelatively driving means for relatively. rotating` the tool element andthe work in direction for withdrawal of the tool element from the work.

rotatable threaded guides, and todiscontinue l relative rotation of thethreaded guides at predetermined torque capacity of the machine;I

It is a further object of the invention to relatively rotate a -toolelement and the work bya clutch engagement; and to actuate the clutch byshiftable means which is tensioned'by its clutch-v engaging shifting,for tensioning clutch engagement; and which is adapted forclutch-disengaging shifting responsive to torque resistance of therelatively rotating tool element and work exceeding tension of theclutch engagement.

It is a further' object of the invention to selectively relativelyVrotate the tool element and the work by one or the other of drivingmeans,

and to rotate the driving means in opposite directions from a commonsource oi rotary power which is adapted for rotation in one direction,there lbeing driving connections between the source of rotary power andthe respective driving means for oppositely rotating the latter,preferably at diiferentspeeds. and lthe work are relatively rotated byone of the drivingmeans the tool element is thus adapt- When the toolelement, I

ed for operative engagement with the work, and

when the .tool' element and the work are relatively rotated by theoppositely rotating driving meansthe tool element is adapted forwithdrawal from the'work.

AIt is a still further object of the invention to 'Further objects ofthe invention tice, it being understood that the form which is shown anddescribed is for purpose of illustra-- transverse sections on .lthe

The invention is particularly applicable and is therefore 4described inconnection with a machine tool in which a tool element is rotated and fed axially relative to stationary work, for threading-the work eitherinternally or externally, e. g. a tapping machine.

As an instance, a spindle frame I on a column 2, and awork table 3 isvertically adjustable on the column.

rotatable inthe frame I'; and is also axially movable relative to theframe and the work table, either manually by a lever 5 or by relativerota-l tion of inter-fitting threaded guides-6 1.

The cooperating threaded guides 6-1 are preferably of the type disclosedand claimed in my copending application Ser. No. 297,697, led October 3,1939; i. e. the guide 6 is a threaded sleeve release the selectivelyengaged driving means atl predetermined torque capacity of the machine.

It is astill furtherobject of the invention to j adjust the releasingpoint for that driving means which relatively rotates the tool elementand the A work in direction for operative engagement, so

as to adjust the torque capacity at which operation of the machine willbe arrested.y

- `1t is a still further vobject .of the invention to release thatdriving means nwhich relatively rotates the tool element and the work indirection for operative engagement, whenv the toolv element has been feda predetermined distance relative to the work, and to then'engage theother which is flxed on the spindle l for rotationandaxial movementtherewith, and the guide 'I is M threaded for engagement with thethreaded l sleeve 6 and is mounted in the spindle i'ramel so that it ish'eld against rotary and axial movement relative to the sleeve. Thethreaded sleeve .ii is rotated and axially displaced with the 'spindle4, for rst cutting a cooperating thread in.v

the guide 1, and thereafter makes threaded engagement with the threadwhich has. been cut in` the guide 1, spindle 4 .in accordance with thelead defined by the thread of the sleeve 6.

As an instance; the threaded sleeve 8 includes a hob 8 for cuttingthreads in the guide 1, and 'a pilot 9 which has a thread correspondingto the will beraad-s4 ily understood from the following description of lthe accompanying drawings which'illustrate a' form which the inventionmay assume in pr'ac- A a vertical sectionfonthe line 5.-5 of ismounted'.

A tool spindle 4 isl for axially feeding the rotating Ipulleys 32--33.

threads which have been cut in theguide 1. Th`e guide 1 preferablycomprises a pair of blocks which engage the sleeve 6 at diametricallyopposite points and which are supported by arms III which are pivotallymounted on a bracket II in the spindle frame I. The arms I are swungrelative to the bracket II by spring levers I2, which are connected vialinks I3 to an actuating rod I4.

A spring I tends to project the rod I4 so as to swing the levers IZ'to aposition in which the blocks 1 are clear of the sleeve 8 as shownat Fig.4; and the rod I4 is adapted for retraction against the tension of thespring I5 for swinging the levers I2 to position engaging the blocks Iwith the sleeve B, with the spring tension of the levers urging theblocks into snug threadedengagement with the sleeve. 'I'he rod I`4 isadapted for retraction by energizing an electrical solenoid I6 which ismounted in the spindle frame I.

A collar I3 is mounted on the spindle 4 for rotation of the spindlerelative to the collar and axial displacement of the spindle with thecollar; and a pair of levers I9 are pivoted to the collar I8, with theopposite ends of the levers pivoted in the spindle frame I at a linkconnection 20.

The levers I9 are thus adapted for swinging movement responsive to axialfeed of the spindle 4 by relative rotation of the cooperating threadedguides 5-1. 'I'he levers I9 are also adapted for swinging movement foraxially displacing the spindle 4, by manually swinging the lever 5. Forthis purpose, the lever 5 is fixed to a transverse shaft 2i which isjournaled in the spindle frame I, and a lever 22 is xed to the shaft 2|and isV connected by a link 23 to one of the levers I9.

Axial displacement of the spindle 4 is counterbalanced. For thispurpose, the levers I9 straddle the upper end of the column 2; and acollar 25 is slidable in the upper end of the column 2 and is connectdby pivot pins 26 to the levers I9, the pivot pins extending throughvertical slots 21 in the wall of the column 2. A rod 28 projectslongitudinally into'the column 2 through the collar 25, and has a collar29 fixed against rotation on its inner end, with a spring 30 between thecollars 25-29. l

'Ihe rod 28 and the collar 29 are adapted for axial displacement bu-tare fixed against rotation in the column 2; and the tension of thespring 3l! is adjusted by rotating a nut 3| which is threaded on theupper end of the rod 28. The tension of the spring 30 is adjusted forcounterbalancing the spindle 4, preferably so that the spindle justtends to shift upwardly in the spindle frame I.

slots 31 in the sleeve 35, into cooperating slots 38 in the spindle. Theslots 31 are of a length permitting axial movement oi the clutchrelative to the sleeve 35 for selectively engaging the cooperatingfriction faces 32a-34a or the cooperating friction faces 33h-34h. Theslots 3l are of a length permitting desired axial displacement of thespindle 4 relative to the spindle frame and the work table, whilemaintaining engagement between the keys 36 and the slots 38.`

'I'he clutchf 34 is actuated by an operating lever which intermediateits ends is pivotedin the spindle frame I as shown at 4I, with a yoke 40at one end of the lever operatively engaging the clutch, and with theother end of the lever comprising an arm 43 which is adapted to be swungfor shifting the yoke so as to axially shift the clutch to operativelyengage it with one or the other of the pulleys 32-33.

The pulleys 32-33 are driven by pulleys 45--43 via belts 41-49; and thepulleys 45-49 are driven in opposite directions from a common source ofrotary power which rotates in one direction. As an instance, an electricmotor 49 isv mounted at the rear of the spindle frame I, and

the pulley 45 is ilxed on the shaft of the motor,

directions by pulleys 32-33 which are journaled on the spindle in theframe I, there being aclutch 34 between the pulleys, iixed for rotationwith the spindle and adapted for axial shifting for frictionallvengaging one or the other of the 34 is mounted on the sleeve 35 betweenthe pulleys, and has friction faces 34a-34h adapted to selectivelyengage cooperating friction faces 32a-33h of the pulleys 32-33. i

The clutch is fixed against rotation relative to the spindle 4, by keys36 which project through while the pulley`46 is fixed on a countershaftIII which is drivenby the motor shaft via speed reduction and reversinggearing 5I.

The arm 43 of the operating lever is swung in opposite directions byselectively energizing electrical solenoids 53-54, for shifting the yoke40 for selectively engaging the clutch 34 with one or the other of thepulleys 33'-32.`

When the arm 43 is actuated by energizing the vsolenoid 53, the yoke 40is shifted so that the clutch 34 engages the pulley 33, therebyrotatingthe spindle 4 via speed reduction gearing 5I, in

vdirection for operatively engaging a tool element engages the pulley32, thereby rotating the spindle 4 in the opposite direction and athigher speed than when the spindle is rotated by the pulley 33, forreversely rotating the tool element relative to the work.

As an instance, the solenoids 53-54 are mounted in the spindle frame Iwith their cores 53a-54a projecting toward one another and connected bya pair of links 51; and the end of the arm 43 is straddled by the links51 and is mounted between transverse pins 58 which connect the pair oflinks. The weight of the cores of the solenoids is counterbalanced,preferably by a spring 59, so that when the solenoids 53-54 l aredeenergized the arm 43 assumes neutral position as shown at Fig. 1,thereby shifting the yoke As an instance, a sleeve 35 is 40 so that theclutch 34 is disengaged from both of the pulleys 32-33.

'I'he operating lever is arranged so that when its arm 43 has been swungfor operatively shifting the yoke 40, said shifting of the yoke isspring tensioned so as to tension the frictional engagement of theclutch 34 with one or the other of the pulleys 32-33, and while the arm43 remains swung to its operative position the spring tensioned yoke 40is adapted to yield for releasing the frictional engagement of theclutch at predetermined torque capacity of the machine, for releasingthe rotary driving connection for the spindle 4.

When the-arm 43 is swung in the.

As aninstance, the arm 43 o; the operating lever is `a leaf-spring,whereby initial swinging of the arm by the energized solenoid 63 or 54shifts the yoke 40 .so as to frictionally engage the clutch, and afterthe clutch has been engaged continued .swinging of the spring 4arm bytheenergized solenoid ilexes the spring arm so that it tensions engagementof the clutch. With the spring arm then retainedin its swung position f."by the energized solenoid, it remains iiexed and tensioned forvmaintaining tension at the clutch engagement; and while thus retainedin its swung position the tension of the exed spring arm is adapted toyield and thus permit shifting of the yoke for releasing the clutchengagement,

the position snewn at Fig.v 1, ready for repeating' responsive tolpredetermined excessive torque. at

the frictionedclutch engagement.

Means are provided f or adjusting the'tension V of thespring arm 43 whenit has been actuated by energizing the 'solenoid 53, i e..when it hasbeen actuated for frictionally engaging the faces 33h-34h so as torotate the spindle 4 in direction for operative engagement oil the toolelement with the work. The frictional engagement' at 33h-34h lmay thusbe adjusted by varying the tension of the spring arm 43, for yielding ofthis e `frictional. engagement and release of the driving connection-via' pulley 33, at .desired torque.

capacity of the machine.

For this purpose, the solenoid 63 is adjustable longitudinally of.v itscore 53a, for adjusting swinging and iiexing of the lspring arm` 43' bythe -energized solenoid, and thus adjusting. the tension exerted by theflexed arm. As an instance, the solenoid 53 is `slidable in a verticalguideway 60 inthe spindle frame I, and is vertiknob 62 at the, exteriorof the spindle frame.

When the machine ris not in operation, the partsare inA thepositionshown at Fig. 1; i`. e. the motor 49 is at rest, the solenoids 53-54 aredeenergized so that the clutch 34 is` in neutral position, and thesolenoid I6 is deenergized .so

cally adjusted by a screw 6I which has acontrol p the cycle. of4operation by again actuating 4the control switch 64. I As shown inFigs. 5 and6, the electrical controlincludes normally open electricalswitches 65--66 whichare` respectively closed when en gaged by an arm61, the switches and their 'co operating arm being preferably housed inal casing 68 which depends from the rear o! the spindle frame I'. Thearm 61 is pivotally mounted at 61a and is swung, in opposite directionsby a link 69. The link 69 .is connected to a -leverlII which is ilxedtoand-projects rearwardly from the transverse shaft 2|, within the spindleframe I. The arm 61 is thus swung 'in one direction (Fig. 5) when thespindle 4 is axially retracted y from the table 3; and the arm 61 isswung in the opposite direction ywhen the spindle 4 is axially projectedtoward the work table.

The,4 switches 65-66 are mounted on arms l1I-l2 which are pivotallyadjustable at I3-14. As .shown at Fig. 5, the arm 1I is pivotallyadjusted sovv that tlieV arm 61 engages and closes the switch 65 atpredetermined limit of upward travel of the spindle 4, and the arm 12 ispivotally adjusted so that the arm l61 engages and closes the switch 66at predetermined limit of downward travel of the spindle. The arms .1I--12 'may be pivotally adjusted by worm-gear connections 15-16, whicharerespectively actuated via driving y connections 'I1-18, by controlknobs 19-60 at the exterior of the casing 66.

The electrical circuit may be arranged as shown at Fig. 7.

Electrical energy is supplied via leads'84-85 l and thencevia the masterswitch 63 which is closed when the machine is to be operated.

a vthereby energizing the `motor 49. Thecontrol thatthe guide blocks 1are swung clear of ,the

^ spindle 4 in direction -for operative -engagement vof the tool elementwith the work. The rotating spindle 4 is thus fed axially by thethreaded engagement 6--1'for operatively engaging. the

tool element with the work, e. g. tapping the' work.` l

When the spindle 4 has been axially .fed the desired distance, e. g,when 'the work has b'een tapped to the desired depth,y the solenoid I3is deenergizedand the v,solenoid 64 is energized,

thereby engaging theclutch 34 with-the pulle'y 32 'forreversely-rotating the spindle 4 so that", -th'e threaded engagement,6-1 reversely feeds the spindle 4 for retraction of the tool element4from the work. When the tool eleirientvis clear4 of the work, thesolenoid 54 is deenergized. whereby the clutch 34 returns to neutralposition for arresting rotation oi' the spindle`4; and

the solenoid I6 is deenergized so thatthe threaded guide blocks 1 areswung clear of the cooperating threaded guide 6. v'llheparts are thusagain in switch 64 is normally open and controls a relay.

66 which when deenergized closes a switch .86a and opens a switchb.Withjzhe control switch 64 in normal open position'fclosing the masterswitch 63 energizes a pilot relay 8l via the closed switch 86a and via anormally closed switch 92a;

and when the pilot relay 81 is thus energized'. it

. closes normally open switches 31a-81h.

The spindle 4 being at its upper limit of travel,

Y with the switch 66 in normal open position and I cuit; Aand closingthe switch 36h energizes a relay the arm Ellengaging and closing theswitch .65, the cycle of operation is started by Aclosing the controlswitch 64. This energizes the relay 86, thereby opening the switch 66aand closing the switch 86h. Opening the switch 86a does not -v break thecircuit for the pilot relay v3'l, since the closed switch 31a nowmaintains this. cir- 66 via the closed switch 61h. Energizing the relay86 closes the normally open switches BSc-86h.

The control switch 64 may then be released for spring .retraction tonormal position (thereby deenergizing the relay 66 and returning thelswitches 6Go-66h to"normal closed and open positions respectively),since the closed "switch 33a now maintains the circuit for .the relay88.

The switch 38h thus remains closed, Ifor continuing the cycle ofoperation to completion.

. The close'd switch 66h energizes the solenoid I6 for operativelyengaging vthe cooperating threaded lguides 6 1; and the closed switch88h also energizes the solenoid' 53'via a normally closed switch a,while the circuit for the solenoid 54 remains interrupted at a normallyopen switch 90b. The clutch'34 is thus actuated for the spindle 4via'the'pulley 33, i. e. for rotating the spindle. and axially feedingit by the cooperating threaded guides 6 1, for tapping engagement of thetool element with the work. This axial feed of the spindle 4 swings thearm 61 so as to disengage it from the switch B3; and this switch, aswell as the switch 88, are thus in normal open position during downwardfeed of the spindle 4.

At predetermined limit of downward feed of the spindle, as determined byadjustment of the arm 12, the arm 61 engages and closes the switch 68.Closing the switch 66 energizes relays 39-80. Energizing the relay 89closes aswitch 89a in a holding circuit 9| for the relays 88 3li; andenergizing the relay 90 opens the normally closed switch 90a and closesthe normally open switch 90b. The solenoid 53 is thus deenergized andthe solenoid 54 is energized, thereby reversing rotation and axial feedof the spindle 4 for threaded retraction of the tool element from thetapped work. This retraction of the spindle 4 swings the arm 61 so as todisengage it from the switch 66, and this switch, as well as the switch85, are thus in normal open position during retraction of the spindle.However the closed switch 89a continues to energize the relays 89 90 viathe holding circuit 9|, and the switch 90b thus remains closed forenergizing the solenoid 54 so as to continue retraction of the spindle4.

At predetermined limit of retraction of the spindle, as determined byadjustment of the arm 1I, the arm B1 engages and closes the switch 65.Closing the switch 85 energizes a relay 92 via the closed holdingcircuit 8l; and energizing the relay 92 opens the normally closed'switch 92a. 'I'he relay 81 is thus deenerglzed, thereby opening theswitches Mci-31h: and the',open switch 81D deenergizes the relay B8,thereby opening the switches iSd-33h.

Opening the switch 33h deenergizes the solenoids i8 and -l4,'withthe'solenoid 53 remaining deenergizedmnd also deenergizes the relays 89-90-32. Deenergizing the solenoid I6 disengages the cooperating threadedguides 8 1; and deenergixing the .solenoid 34 returns the clutch 34 toneutral position, disengaged from both the pulleys 3I l3. Deenergizingthe relay 89 opens the A vided, with a normally open switch 34 in thiscircuit. At any point during downward travel of the spindle 4, theswitch 94 .may be closed at the will of the operator. This energizes therelays 43-03, thereby closing the switch 39aand opening the normallyclosed switch 80a and closing the normally open switch 90b as previouslydescribed, for deenergizing the solenoid 53 and enersizingthesolenoid 54so as to reverse the rotation and axial feed of the spindle 4 forwithdrawal of the tool element from the work. When the spindle hasreached predetermined limit of withdrawal. with the emergency switch 94having been released for spring retraction tonormal open position, thearin 81 engages and closes the switch 65, thereby completing thefcycleof operation as previously described.

a hob 8 and a pilot thread 3 corresponding .o the desired tappingoperation by the tool element which is mounted in the chuck 53; andblocks 1 with no threads cut therein are mounted in the arms l0. Thespindle 4 is axially shifted by the lever l so that the lower end of thehob 8 is alined with the blocks 1; and

operation of the machine is started by closing pivotally adjusted bytheir control knobs 19-80, j so that during the cycle of operation andthroughf out the range ofaxial displacement of the spindie 4 thethreaded blocks 1 will be transversely alined with the pilot thread .3.The electrical control -is thenactuated as previously described, therebyengaging the threaded blocks 1 by the interfitting pilot thread 3 androtating the spindie 4 by the pulley 33. The rotating spindle 4 is thusfed downwardly bythe interfltting and relatively rotating threadedguides 6 1, so that the tool element which is mounted in the chuck 5Bwill correspondingly tap the work on the By adjusting the spring 30, thespindle 4 is counterbalanced so as to relieve the intertting threadedguides 6 1 of axial strain, thereby adapting the spindle for precisionfeed by the interfltting and relatively rotating threaded guides; and byvertically adjusting the solenoid 53 relative to its core 53a, thefrictional engagement at 32a 34a is adjustably tensioned` so that duringthe tapping operation this frictional engagement will yield atpredetermined torque capacity of the machine, thereby arrest--` ingrotation of thespindle 4 and thus arresting tapping feed of the toolelement, due to relative rotation of the intertting threaded guides 4 1on the machine at any place (not shown) where' it is accessible forstarting or stopping the cycle of operation.

I claim:

v1. Ina machine tool; a rotatable spindle; a

rotary driving means; a clutch between the spindle and the drivingmeans; a lever having a yoke shiftable for engaging. or disengaging theclutch, an arm having an actuating end shiftable to operative position,and a spring connection adapting the yoke and the actuating end of thearm for relative movement for tensioning the spring connectionresponsive to shifting the actuating end of the arm to operativeposition; the tensioned spring connection shifting the yoke for engagingthe clutch and adapted to yield responsive to torque resistance of thespindle \ex ceeding tension of theV spring connection, for

clutch-disengaging shifting of the yoke while the actuating end of thearm is retained in operative *v yoke and having an actuating endshiftable to. .operative position; the leaf-spring arm being adapted forflexing for tensioning the arm and shifting the yoke for engaging theclutch responsive to shifting the actuating end of the arm to operativeposition; the exed andtensioned leaf-spring arm being adapted to yieldresponsive to torque resistance of the spindle exceeding tension of thearm, for clutchdisengaging shifting of the yoke while the actuating endof the arm is retained in operative position; and-operating means forvshifting and retaining the Aactuating end of the arm in operativeposition.

3. In a machine tool; )a rotatable spindle; a rotary driving means; aclutch between the spindle and thedriving means; A a lever having a yokeshiftable for engaging or disengaging the clutch, an arm having anactuating end shiftable to -operative position, and a spring connectionadapting the yoke and the actuating end of the arm for relative movementfor tensioning the spring connection responsive to shifting theactuation end of the arm to operative position; the tensioned springconnection shifting the yoke for engaging the clutch and adapted toyield responsive to torque resistance of the spindle exneeding tensionof the spring connection, for

clutch-disengaging shifting of the yoke while the actuating end of thearm is retained in operative position; operative means for shifting andretaining the actuating end of thev arm in operative position; and meansfor adjusting the clutch-engagingl tension exertedby the tensionedspring connection.

4. In a machine tool; a rotatable spindle; a rotary driving means; aclutch between the spindle and the driving means; alever having a yokeshiftabl for engaging or disengaging the clutch and a; leaf-spring armfor shifting the yoke and having an' actuating end shiftable tooperative position; the leaf-spring armbeing adapted for flexing fortensioning 'the arm and shifting'the yoke for engaging thel clutchresponsive to shifting the actuating end of the arm to operativeposition; the flexed and tensioned leaf-spring arm being4 adapted toyield responsive to torque resistance of the spindle exceeding tensionof the arm, for clutch-disengaging shifting of the yoke while theactuating and means for adjusting the operating means CFI so as tovarythe flexing ofA the leaf-spring arm for adjusting the clutch-engagingtension exerted by the iiexed arm.

5. In a machine tool; a rotatable s'pindlef a rotary driving means; aclutch between the spinvcile and the driving means; a. lever having ayoke shiftable for engaging or disengaging the clutch, an arm having anactuating end shiftable to operative or inoperative position, and aspring connection adapting the yoke Aand the actuating end of the armfor relative movement for tensioning the spring connection responsive toshiftlng the actuating end of the arm to operative position; thetensioned spring connection shifttion, forclutch-disengaging shifting ofthe yoke ing the yoke for engaging the clutch and adapted to yieldresponsive to torque resistance of. the spindle exceeding tension of thespring connecwhile the actuating end of the arm is retained in operativeposition, and the tensioned spring connection being adapted for reliefof its tension and shifting of the yoke for disengaging the clutch,responsive to shifting the actuating end of the arm toits inoperativeposition; and operating means for selectively shifting and retaining theactuating end of the arm in operative or inoperative position.

6; In a machine tool; a rotata le spindle;

driving means `rotating in opposite irections; a

clutch between the spindlef and the driving means; a lever having a yokeshiftable for selectively engaging theclutch with the respective drivingmeans or disengaging the clutch from both driving means; an armhaving anactuating end selectively shiftable to operative posi-,-

tions or to an inoperative position, and a spring connection adaptingthe yoke and the actuating end of .the arm for relative movement fortensioning the Ispring connection responsive to shift- .ing theactuating end of the arm to either operative position; the tensionedspring connection shifting the yoke for selectively engaging .the clutchin accordance with the selected operative position of the "actuating endof the arm, and

adapted to yield responsive to torque resistance of the Aspindleexceeding tension of the spring connection, for clutch-disengagingshifting of the yokel while the actuating end of the arm is retained inselectedv operativel position, and the tensioned spring connection beingadapted for relief of its tension and shifting of the yoke fordisengaging the clutch, responsive to shifting the actuating end` of thearm to its inoperative position; an'd operating means for selectivelyshifting and retaining the actuating end of the arm inioperative or ineither operative position.

l HARDING F. BAKEWELL.

